In effect, piloting any aircraft entails knowing its relative speed in relation to the air, that is to say to the relative wind. This speed is determined using static pressure Ps and total pressure Pt measurement probes. The total Pt and static Ps pressures provide the modulus of this speed vector.
As is known, the total pressure Pt can be measured using a so-called Pitot tube. This is a tube that is open at one of its ends and blocked at the other. The open end of the tube substantially faces into the flow. The stream of air situated upstream of the tube is progressively slowed down until it reaches an almost zero speed at the tube inlet. The slowing down of the speed of this stream of air increases its pressure. This increased pressure forms the total pressure Pt of the flow of air. The principle of such a total pressure measurement probe is recalled in FIG. 1. The probe 10 is intended to be fixed through an opening 11 produced in the skin 12 of an aircraft. The probe 10 comprises a part 13 that is external to the skin 12 and formed by a Pitot tube 14 borne by a strut 15. The probe 10 also comprises an internal part 16 essentially comprising an electrical connector 17 and a pneumatic connector 18. The connector 17 makes it possible to electrically connect the probe 10 to the aircraft, for example to connect heating means for the deicing of the probe 10. The connector 18 allows for the pneumatic connection of the Pitot tube 14 to a pressure sensor or other measurement device, situated inside the skin 12 of the aircraft. The probe 10 is positioned on the skin 12 of the aircraft such that the Pitot tube 14 is oriented substantially on a longitudinal axis of the aircraft, excluding laminar boundary layer, for the direction of the flow, embodied by an arrow 19, to substantially face an inlet orifice 20 situated at a first end 21 of the Pitot tube 14. In the example represented, the Pitot tube 14 is fixed relative to the skin 12 of the aircraft. It is of course possible to mount the Pitot tube 14 on a moving strut such as, for example, a paddle that can be oriented in the axis of the flow as is, for example, described in the patent published under the number FR 2 665 539.
In practice, the flow of air can convey solid or liquid particles, such as, for example, the water from the clouds, that are likely to penetrate into the Pitot tube and build up in the tube at the blocked end. To prevent such a build-up from disturbing the pressure measurement, one or more drain holes and water traps are generally provided, to avoid any risk of obstruction of the ducts responsible for transmitting the total pressure to the pressure sensors situated inside the skin of the aircraft or to the instruments of the aircraft instrument panel. As represented in FIG. 2, the Pitot tube 14 thus comprises, in proximity to an end 22, a drain hole 23 that makes it possible to discharge particles likely to penetrate inside the tube 14. Still at the end 22 of the tube, an air line 24 opens into the tube 14 to form therein a pressure tap 40 at which the air pressure is to be measured. The pressure tap 40 is generally constructed in such a way as to avoid the ingestion of water into the tube 14 and thus form a water trap. The line 24 is, for example, linked to a pressure sensor not represented in FIG. 2. The pressure sensor makes it possible to effectively measure the pressure of the air prevailing inside the tube 14 at its end 22. Apart from the drain hole or holes 23, the sections of which are small compared to that of the tube 14, the tube 14 is closed at its end 22. The pressure measured at this end therefore represents the total pressure Pt of the flow of air.
The drain holes make it possible to discharge the liquids and any particles that may penetrate into the tube. The slowing down of the air in the tube is therefore not complete and the total pressure Pt measurement is affected. More specifically, the greater the efforts that are made to avoid the build-up of water or of particles of significant size, the more the total pressure measurement is affected by increasing the dimensions or the number of drain holes. Conversely, the greater the efforts to improve the total pressure Pt measurement by reducing the dimensions or the number of drain holes, the greater the risk of build-up of water or of particles. With a Pitot tube, there therefore has to be a trade-off between quality of the total pressure Pt measurement and risk of disturbance of the measurement because of the penetration of water, or of particles conveyed by the flow of air where the measurement is performed.
In the operational life of aircraft, the drain holes can be polluted, because of the ingestion of dust, insects, plant residues or other foreign bodies. Because of their size and the position of the Pitot tubes on the fuselage of an aircraft, the periodic checking of the integrity of the drain holes is difficult.
The checking of the drain holes of the Pitot tubes is generally done visually. The operator responsible for maintaining the aeroplanes inspects the drain hole or holes using a small lamp. If foreign bodies are observed, the probe is dismantled, and its pneumatic circuits cleaned. This operation is all the more difficult when the aeroplane is of large size. Access to the probe and to the drain holes whose diameter is generally less than 1 mm is difficult.
Also known from the applicant is a checking device intended to be temporarily connected to the pressure measurement probe, and that makes it possible to check, using an acoustic transmitter and an acoustic receiver, the non-blocking of the internal cavities and the drain holes of the probe. The principle of such a device is notably described by the patent published under the reference FR 2 959 822. It is also recalled by FIG. 2 of this application. The checking device 25 comprises a transmitter 26 and a receiver 27 intended to be connected to an internal volume 30 of the probe, formed by the inside of the tube 14, the drain hole or holes 23 and the line 24. The transmitter transmits an acoustic signal that is propagated in the internal volume 30 and the receiver is configured to pick up an acoustic signal observed in the internal volume 30. The device also comprises processing means 28 that make it possible to compare the acoustic signal observed in the internal volume to a reference acoustic signal measured on a probe that is not clogged, in order to establish the presence of particles in the internal volume.
The principle of the device is therefore based on a characterization of the architecture of the internal volume, by means of a measurement of the internal acoustics of the probe. The detection of pollution or of clogging of the drain holes is based on the comparison of this measurement with a reference signal measured on a non-clogged probe. It will be understood that an incorrect connection of the probe alters the internal acoustics measured by the device. The comparison of an acoustic signal measured for a probe incorrectly connected to the device, to the reference signal, can thus incorrectly conclude that the drain holes of a probe are clogged. To ensure an effective check, the connection of the device with the probe has to be reproducible. It is also desirable to have means that make it possible to check the reliability of the connection with the probe.